In the fall of 1979, a furor erupted in the United States over the discovery of Soviet combat troops in Cuba. Scarcely remembered today, it was an episode of the Cold War that seemed like a very big deal at the time, so much so that it prompted U.S. president Jimmy Carter to address the American people on nationwide television.

Ultimately, it was an uproar over practically nothing, but it helped derail a major nuclear arms agreement between the United States and the Soviet Union and signaled that the era of détente between the two countries was coming to an end.

Cuba had been a bugaboo of U.S. policymakers since the communist revolution that put Fidel Castro in power in 1959. The widespread American fear that the USSR would use the island nation as a foothold from which to threaten the United States in its own hemisphere reached its high point in October 1962 during the Cuban Missile Crisis, but it didn’t end there.

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On Sept. 16, 1970, an American U-2 reconnaissance aircraft detected evidence that the Soviet Union was constructing a long-term naval facility at the Cuban port of Cienfuegos, one which could serve as a permanent base for Soviet ballistic missile submarines. U.S. officials in the Nixon administration raised objections with Moscow, stating that such a move would contravene the USSR’s commitment following the Cuban Missile Crisis to refrain from introducing offensive military forces into the Western Hemisphere.

The Soviets, who denied that they were building such a base, ultimately withdrew the submarine tender and two support barges it had sent to Cienfuegos and for the most part the matter died down.

Another, more minor controversy arose in November 1978 when it came to light that the Soviet Union had provided Cuba with between 12 and 24 MiG-23 fighter-bombers seven months earlier. These were tactical aircraft, not strategic bombers, but they were capable of carrying nuclear weapons.

However, U.S. intelligence quickly determined that the Cuban MiG-23s were not nuclear capable. Officials in the Carter administration assured the public that there was no evidence of Soviet nuclear weapons being present in Cuba and that the MiGs were too few in number to pose a military threat to the United States.

The 1979 crisis arose not because of any specific action taken by the Soviets or the Cubans, but because of a reexamination of existing information already held by the U.S. intelligence community. Concern had been mounting for some time in the United States about Soviet-Cuban support for pro-communist forces in Latin America. In March, National Security Advisor Zbigniew Brzezinski ordered Stansfield Turner, then Director of Central Intelligence, to undertake an overall assessment of Soviet forces present in Cuba.

The review, completed in July, determined that there was what appeared to be a brigade-size contingent of Soviet combat troops on the island, one that was separate from the Soviet training mission that the United States had long known was there.

It was unclear what the unit’s purpose was, but its presence represented a new and disconcerting discovery, one that was bound to create a stir in Washington. Rumors of the report’s findings began to surface in late summer, and the Carter administration decided at the end of August to begin informing key members of Congress.

What followed was a textbook example of a political crisis almost entirely devoid of substance. The presence of 2,000 to 3,000 Soviet combat troops in Cuba was unacceptable to many Washington leaders, both Republican and Democrat.

Sen. Frank Church, a liberal Democrat from Idaho who served as the chairman of the Senate Foreign Relations Committee, immediately demanded the brigade’s removal. “The United States,” he said on Sept. 4, “cannot permit the Soviets to establish a military base on Cuban soil, nor can we allow Cuba to be used as a springboard for real or threatened Russian military intervention in the hemisphere.”

Sen. Richard Stone of Florida echoed this sentiment, arguing that the brigade’s deployment violated the Monroe Doctrine. Howard Baker, the Republican leader in the Senate, stated that if the U.S. tolerated the presence of Soviet combat troops in Cuba, “we will in effect be letting the Soviet Union thumb their noses at us.”

Ronald Reagan, preparing for his run for the presidency in 1980, said that the United States “should not have any further communications with the Soviet Union” until the troops were withdrawn.

When the news broke, the Carter administration scrambled to get ahead of the issue. It faced the difficult task of persuading Congress and the general public that it was taking the situation seriously without further fanning the flames of alarm. On Sept. 5, Secretary of State Cyrus Vance told reporters that “the presence of this unit runs counter to long‐held American policies.”

Two days later, the president called a news conference and stated that “this status quo is not acceptable.”

But the newly discovered Soviet troops were not new at all. According to U.S. intelligence, they had been present in Cuba since at least 1976, and possibly much longer than that. Moreover, it was widely understood at the time – even by those who voiced the most alarm at the discovery – that the small Russian force posed no military threat to the United States.

It consisted of a headquarters unit, a tank battalion and three motorized rifle battalions, but it had no air- or sea-lift capability and there were no indications that it was equipped with nuclear weapons. So why was its discovery in Cuba so distressing to U.S. political leaders?

The uproar over the Soviet brigade arose at a pivotal time. The preceding decade had witnessed a substantial thaw in relations between the United States and the USSR, a period commonly known as détente. By the end of the 1960s, both superpowers were ready to move away from the tensions that had characterized the first 20 years or so of the Cold War, a time when it often seemed that war could break out at any moment.

The United States was bogged down in a difficult and unpopular war in Vietnam while the Soviet Union found itself facing a major new threat from China following the Sino-Soviet split. Moscow and Washington both recognized that while the two nations were not friends, they could work together in some areas to mutual advantage.

One of those areas was arms control. In 1969, the two superpowers began strategic arms limitations talks, or SALT, to curb the ongoing nuclear arms race. Three years later, they reached an agreement that froze the number of ICBMs and SLBMs that each side could possess. The SALT I accord was an interim arrangement intended to set the stage for a new round of negotiations known as SALT II.

It did not place any limits on the number of warheads the two nations could deploy on their missiles, nor did it impose any constraints on the size of either nation’s conventional military. It was, however, hailed as an important step forward in improved U.S.-Soviet relations.

There were other aspects of détente, too. The two nations agreed to limit their ballistic missile defenses and spearheaded the signing of a global agreement to cease production of biological weapons. Trade between the U.S. and Soviet Union increased, as did scientific and cultural exchanges. To many observers in the 1970s, the improvement in U.S.-Soviet relations seemed permanent. Indeed, it was common at the time for people to refer to the Cold War in the past tense.

In retrospect, however, it is clear that détente represented only a temporary lull in the Cold War, not the end of it. The United States and the Soviet Union remained geopolitical and ideological rivals, even if the intensity of their competition appeared to have lessened.

From the American perspective, there were two main reasons why détente began unraveling in the second half of the decade. One was the ongoing Soviet military buildup. Soviet conventional forces expanded throughout the 1970s while the American military contracted as part of the post-Vietnam drawdown. Soviet forces in Eastern Europe underwent a significant modernization effort over the course of the decade and added around 150,000 men.

The Soviet navy, previously only capable of coastal defense, grew from 215 ships to 279 while American naval forces shrank by nearly a third.

Even more worrisome was the growth of the Soviet strategic nuclear arsenal. The United States had enjoyed a decisive lead in nuclear weapons since the beginning of the arms race, but the Soviets sought to close the gap following the Cuban Missile Crisis. During the 1970s, the Soviets began augmenting their nuclear forces by adding multiple independently targetable reentry vehicles to their existing launch platforms, something the United States had already begun doing a few years earlier.

Most of the increase in the USSR’s arsenal occurred in its ICBMs, which were becoming accurate enough to destroy U.S. missiles in their underground silos. A 1977 study by the Congressional Research Service forecast that by the end of the decade the USSR would possess nearly 4,600 nuclear warheads on its fleet of ICBMs, more than twice the U.S. number.